1. Technical Field
This invention relates to novel thermotropic liquid crystalline polyester compositions prepared from hydroquinone, 4,4'-dihydroxybiphenyl, terephthalic acid, 2,6-naphthalenedicarboxylic acid, and 4-hydroxybenzoic acid. The compositions are characterized as having melting points less than 365.degree. C., breaking elongations greater than or equal to 1.5%, and heat distortion temperatures greater than 200.degree. C.
This invention further relates to novel glass reinforced/filled thermotropic liquid crystalline polyester compositions prepared from the same components given above and additionally containing 20 to 40 weight percent of at least one glass reinforcing/filling agent. These glass reinforced/filled compositions are characterized as having melting points less than 365.degree. C., breaking elongations greater than or equal to 2.0%, and heat distortion temperatures greater than 230.degree. C.
The thermotropic liquid crystalline polyester compositions of the present invention and the glass reinforced/filled thermotropic liquid crystalline polyesters of the present invention are advantageous because they have melting points less than 365.degree. C., which allows them to be manufactured and processed without undergoing significant thermal degradation.
The thermotropic liquid crystalline polyester compositions of the present invention are further advantageous because they have braking elongations greater than or equal to 1.5%; the glass reinforced/filled thermotropic liquid crystalline polyester compositions of the present invention are further advantageous because they have breaking elongations greater than or equal to 2.0%. Breaking elongation is a measure of the toughness of a composition and increasing values are highly desirable. Breaking elongations in molded parts greater than or equal to 1.5% (or greater than or equal to 2.0% for 20 to 40 weight percent glass reinforced/filled compositions) are rare in liquid crystalline polyester compositions and are very desirable for many high temperature end-use applications.
The liquid crystalline polyester compositions of the present invention are also advantageous because they have heat distortion temperatures greater than 200.degree. C.; the glass reinforced/filled liquid crystalline polyester compositions of the present invention are also advantageous because they have heat distortion temperatures greater than 230.degree. C. Such heat distortion temperatures make both types of compositions useful for many high temperature end-use applications. Examples of high temperature end-use applications include, but are not limited to, electrical end-use applications, such as those involving assembly with high temperature soldering techniques (such as vapor phase reflow and infrared soldering) and automotive end-use applications.
The thermotropic liquid crystalline polyester compositions of the present invention can be formed into fibers, films, monofilaments, molded articles, and shaped articles. The glass reinforced/filled thermotropic liquid crystalline polyester compositions of the present invention can be formed into molded articles or shaped articles. Both types of compositions are useful in applications where it is desired to use a polymer composition having a high breaking elongation, a melting point less than 365.degree. C., and a high heat distortion temperature.
2. Background Art
U.S. Pat. No. 4,849,499 discloses wholly aromatic polyesters prepared from approximately equimolar amounts of a diacid component, which is a mixture of 2,6-naphthalenedicarboxylic acid and terephthalic acid, and an aromatic diol component comprising 4,4'-dihydroxybiphenyl, and which are modified with 10-80 mole percent p-hydroxybenzoic acid. The reference discloses that minor amounts of additional modifying dicarboxylic acid units, such as isophthalic acid and other naphthalenedicarboxylic acids, and/or aromatic diol monomer units, such as hydroquinone and resorcinol, may be present in the polyesters disclosed therein. However, there is no specific example provided wherein hydroquinone is used in preparing the polyesters exemplified therein. Further, there is no specific teaching that wholly aromatic polyesters prepared from 2,6-naphthalenedicarboxylic acid, terephthalic acid, 4,4'-dihydroxybiphenyl, p-hydroxybenzoic acid, and hydroquinone would have melting points less than 365.degree. C. In fact, none of the polymers prepared in examples 3, 4, and 5 of this reference had a melting point, as measured by DSC, less than 400.degree. C. The polymers of Examples 3, 4, and 5 were all prepared from 2,6 -naphthalenedicarboxylic acid, terephthalic acid, 4,4'-bis-acetoxybiphenyl, and p-acetoxybenzoic acid. There is no indication that the addition of hydroquinone to such polymers would result in the melting point of such polymers being less than 365.degree. C. Further, there is no teaching provided in this reference that the compositions described therein have heat distortion temperatures greater than 200.degree. C. and breaking elongations greater than or equal to 1.5%. There is also no teaching that glass reinforced/filled compositions having high breaking elongations, high heat distortion temperatures, and relatively low melting points can be produced.
U.S. Pat. No. 4,169,933 discloses liquid crystalline polyesters prepared from terephthalic acid, 2,6-naphthalenedicarboxylic acid, a diacyl ester of hydroquinone, and acyloxybenzoic acid. There is no teaching of the use of 4,4'-dihydroxybiphenyl in the polyesters disclosed in this reference. Further, there is no teaching that the compositions described in this reference have heat distortion temperatures greater than 200.degree. C. and breaking elongations greater than or equal to 1.5%. There is further no disclosure in this reference on how to produce a glass reinforced/filled compositions having high heat distortion temperatures, high breaking elongations, and relatively low melting points.
U.S. Pat. No. 4,067,852 discloses aromatic polyesters consisting essentially of recurring units of I, II, and III wherein ##STR1## (I) may be 4-hydroxybenzoic acid, (II) may be 2,6-naphthalenedicarboxylic acid, and (III) may be hydroquinone. This reference specifically teaches away from the compositions of the present invention in that at column 4, lines 25-27, it is stated that "It is essential that moiety II consists of a pair of fused benzene rings . . . rather than a single divalent benzene ring." The reference continues by stating, in column 4, lines 27-34 that "For instance, it has been found that if one were to substitute single benzene rings for a substantial portion of the naphthalene rings of moiety II, the properties of the resulting wholly aromatic polyester would be substantially different and adversely influenced as evidenced by substantially higher flow and melt temperatures resulting in significant degradation on processing." Terephthalic acid, which is a major component of the compositions of the present invention, is an example of a single divalent benzene ring.
U.S. Pat. No. 4,118,372 discloses a broad class of melt-spinnable fiber-forming synthetic anisotropic polyesters and copolyesters having a flow temperature of at least 200.degree. C. The compositions of the present invention are not specifically exemplified in this reference. Further, the reference provides no teaching on how to obtain a liquid crystalline polyester composition having a melting point less than 365.degree. C., a breaking elongation greater than or equal to 1.5%, and a heat distortion temperature greater than 200.degree. C.